Internal combustion engines are frequently equipped with turbochargers. A turbocharger is driven by the exhaust flow of the internal combustion engine, and may compress the intake airflow into the engine in order to achieve more power. Multi-stage intake charging systems with series stages of turbocharger or electric supercharger (ES) systems are adopted to improve the boost response of turbocharged engines. Compared to the turbocharger, the ES has the advantage of delivering boost pressure faster in a shorter response time. For example, an ES typically has a response time (idle to 100% duty cycle) in the 130-200 ms range, compared to 1-2 seconds for a turbocharger.
Ethanol is widely used as a renewable fuel worldwide. However, due to the ultra-low volatility of ethanol at around freezing temperature, vehicles using a high percentage of ethanol as fuel may be difficult to start in cold weather. During vehicle cold start, fuel injected into the engine cylinder may stay in the liquid form and fail to form a combustible air/fuel mixture with intake air. As such, a first combustion of the engine may not be reliably initiated, which may impair drivability, fuel consumption, and exhaust gas emissions.
One example approach to address the issue is shown by Gluckman in U.S. Pat. No. 4,667,645. Therein, during cold start, an intake manifold is warmed up by an intake manifold heater before injecting fuel into an engine combustion chamber.
However, the inventors herein have recognized potential issues with such a system. As one example, the intake manifold heater may take a relatively long time to warm up the intake manifold to a desired temperature. As a result, engine start may be delayed and vehicle drivability may be affected. Moreover, because of thermal expansion of air in the intake manifold, manifold pressure may change during the warmup process. Pressure in the intake manifold may change in response to the ambient temperature and the desired manifold temperature. Thus, intake manifold pressure may vary from one engine start to another and further affect vehicle drivability.
In one example, the issues described above may be addressed by a method for starting an engine, comprising: in response to an engine start request, operating a supercharger to warm up an intake manifold; and adjusting an intake manifold pressure before starting a first combustion of the engine. In this way, the engine may be reliably and quickly started during cold start.
As one example, during engine cold start, an ES is operated to compress intake air in response to an engine start request. The intake manifold may be warmed up by the compressed air. When temperature of the intake manifold reaches a predetermined value, intake manifold pressure is adjusted to a desired level for a first combustion. Temperature of fuel injected into the cylinder may be increased when passing through the warmed up intake manifold. As such, fuel injected during engine cold start may be warmed up without extra heating equipment. Moreover, due to the fast response and high efficiency of ES, engine start time may be shortened. Further, by adjusting intake manifold pressure before initiating the first combustion, engine operating conditions for the first combustion may be accurately controlled.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.